This invention relates to the separation of at least one first hydrocarbon from at least one close-boiling second hydrocarbon by extractive distillation.
Extractive distillation is a well known technique for separating mixtures of components having a relative volatility close to unity (i.e., having nearly equal volatility and having nearly the same boiling point). It is difficult to separate the components of such mixtures by conventional fractional distillation. In extractive distillation, a solvent is introduced into a distillation column above the entry point of the hydrocarbon-containing fluid mixture which is to be separated. The solvent affects the volatility of the hydrocarbon-containing fluid component(s) boiling at higher temperatures (i.e., high-boiling components) differently than the hydrocarbon-containing fluid component(s) boiling at lower temperatures (i.e., low-boiling components) sufficiently to facilitate the separation of the various hydrocarbon-containing fluid components by distillation and such solvent exits with the bottoms fraction, as has been described in the article entitled Extractive Distillation Saves Energy by Ian Sucksmith, Chemical Engineering, Jun. 28, 1982, pages 91-95. Additional information on extractive distillation techniques can be found in Perry""s Chemical Engineers"" Handbook, Sixth Edition, McGraw-Hill, Inc., copyright 1984, pages 13-53 to 13-57.
It is an object of this invention to provide a process for separating at least one first hydrocarbon from at least one close-boiling second hydrocarbon different from said at least one first hydrocarbon by extractive distillation using a selective solvent (also referred to as extractant or entrainer). Other objects and advantages will be apparent from the detailed description of the invention and the appended claims.
In accordance with this invention, a process for separating at least one first hydrocarbon, selected from the group consisting of aromatic hydrocarbons, cycloalkanes, cycloalkenes, cycloalkadienes, and the like and combinations thereof, from at least one close-boiling second hydrocarbon selected from the group consisting of alkanes, alkenes, alkadienes, and the like and combinations thereof by extractive distillation of a hydrocarbon-containing fluid comprising said at least one first hydrocarbon and at least one close-boiling second hydrocarbon by using a solvent comprising a 3-alkyl-substituted-2-oxazolidinone.